Proportional representation is often thought a democratic ideal. But whatever proportional representation's virtues in ordinary politics, it is poorly suited to sustaining democratic legitimacy in what might, speaking loosely, be called constitutional politics. Proportional representation may fairly balance citizens' views concerning incremental policy innovation. But proportional representation succeeds less well at uniting individual citizens' wills into a sovereign decision concerning the basic structure of the social contract. This is not just an abstract problem. Many of the world's most mature democracies (including especially in Europe) face constitutional choices in this loose sense-choices concerning the scope and character of their political orders. At the same time, citizens of the mature democracies are losing confidence in the democratic practices and institutions through which these and other constitutional decisions must inevitably be made. The mismatch between proportional representation and constitutional politics contributes to the current crisis of democratic legitimacy in Europe and, surprisingly, also in the United States. European democracies' explicit embrace of proportional representation makes it natural for the argument to take up the European case. The American case is included in part for its own sake, as the nature and even the existence of an American drift towards de facto proportional representation is not widely appreciated. The American case is also included because it might introduce novel ideas to this Working Paper Series' European audience, which will naturally have attended only casually to recent American developments.